Constant velocity temperature probe in a product flow line

ABSTRACT

A temperature probe for use in a product flow line including a valve seat secured in the flow line, a valve stem and an orifice ring. The orifice ring is attached to the valve stem to define a pair of flow paths for product passing through the product flow line. One flow path is through the ring and the other is between the ring and the valve seat. A temperature sensing probe is carried by the valve stem and positioned in the orifice ring for sensing the temperature of the product in the flow line. A spring is connected to act on the valve stem and is responsive to changes in velocity of the product in the flow line to move the orifice ring toward and away from the valve seat to maintain the velocity of the product flowing past the probe constant.

This invention relates to temperature probes, generally, and moreparticularly to such probes which are useable in sensing the temperatureof flowable products.

The process control systems employed in the processing of flowable foodproducts, such as tomato paste and salad dressings, for example, requirethe input of data regarding the product's temperature. Such temperaturedata must not only be accurate but also provided continuously. It hasbeen common practice to position any one of a variety of temperatureprobes where it projects into the product sensed, with the mostefficient position being in a flow line carrying the product so that theflow of the product past the probe provides the most current temperaturedata for use by the process control system. Such an arrangement willprovide a continuous stream of temperature data, but accuracy becomes aproblem when the product has a high viscosity and a tendency tocoagulate causing the product to adhere to and build up, i.e.,accumulate, on the probe. Such build up creates a static boundary layerwhich acts as insulation decreasing the sensitivity of the probe. As aconsequence, the process control system receives temperature data thatis not accurate. While the mere velocity of the product flowing past theprobe will discourage such build up, the process control system itselfmay create variations in the product flow resulting in inconsistentvelocities across the temperature probe. Since some food products, suchas tomato paste, for example, exhibit properties which are thixotropicin nature, i.e., their viscosity increases as the velocity of their flowdecreases, it is desirable to maintain a constant velocity past thetemperature probe even though the process control system createsvariations in the flow rate through the system. It is even possibleunder extreme conditions for the combined effects of build up and thevariations in the system flow rate to result in temperature data that isso inaccurate that it causes the control system to lose control of theprocess itself

The present invention provides a temperature probe mounted in the centerof a streamlined orifice ring which is movable toward and away from avalve seat to define a predetermined, fixed-area path for product flowthrough the center of the orifice ring and a variable-area path betweenthe orifice ring and the valve seat, with flow being blocked from thelatter path when the orifice ring is in engagement with the valve seat.A spring is operatively connected to the orifice ring to urge theorifice ring toward the valve seat. The position of the orifice ring isdetermined by the opposing force of the velocity head created byimpingement of the product flow against the orifice ring and the frontalarea of the temperature probe. Thus, as the velocity head increases as aresult of an increase in the flow of product through the system, theorifice ring will move away from the valve seat. The increased area ofthe variable path permits greater flow of product therethrough so thatthe velocity of product through the fixed-area path remainssubstantially unchanged. Conversely, as the velocity head decreases as aresult of a decrease in the flow of product through the system, theorifice ring will move toward the valve seat decreasing the area of thevariable path and assuring a greater percent of the system flow isthrough the orifice ring in order to maintain the velocity of productflow past the temperature probe substantially constant. Thus, thevelocity of product flow through the orifice ring and past thetemperature probe will remain substantially constant even thoughvelocity of product flow through the system varies.

The objects of the present invention are to provide a temperature probewhich solves the problems encountered with, and shortcomings of, priorart probes; which provides an accurate indication of the temperaturethrough a wide range of variations in product flow through the systemeven when sensing viscous or thixotropic products; which effectivelyprecludes the build up of product thereon; which maintains an optimumvelocity of product flow across the probe throughout a wide range ofsystem flows; which may be readily retrofitted into existing systems;and which is reliable and easy to maintain. These and other objects ofthe present invention, and many of the attributes thereof, will becomemore readily apparent from a perusal of the following detaileddescription and the accompanying drawings, wherein the sole figure is avertical cross section of a product flow line incorporating atemperature probe according to the present invention.

Referring to the drawing, a portion of a product flow line is shownincluding a straight section 10 and a ninety degree elbow 12, sealinglyclamped to each other by means of connectors, which for clarity have notbeen shown, but are standard connectors such as those sold byCherry-Burrrell, for example, that engage and squeeze the adjacentangled protrusions, with the flow of product therethrough being from thesection 10 into the elbow 12. A valve seat 14 is formed on the upstreamend of the elbow 12. An orifice ring 16 is attached to threeequi-angularly spaced support arms, two of which are shown at 20, whicharms are attached to a streamlined, cylindrical body 19. The body 19 isthreadedly secured at one end to a hollow valve stem 18 and has anopening at is forward end. The valve stem 18 extends through and isslideable in a bushing 22 pressed into a bore formed in an insert 24sealingly clamped by a means of a standard connector to an extension 13formed on the elbow 12. A temperature sensing probe 27, which preferablyis a resistance thermal detector (RTD), but may also be a thermistor, abimetallic thermometer, a thermocouple or a mercury thermometer, has atemperature sensitive tip 26 formed in situ with a larger diametersheath 29. The probe 27 is positioned inside the hollow valve stem 18with the tip 26 centered on the orifice ring and the end of the tippositioned at the minimum interior diameter of the ring 16. The probe 27is releasably locked in this position by a clamp arrangement, whichincludes a circular plate 50 threaded onto a fitting 52 secured to theouter end of the sheath 29 and a split clamp 54 engaging an exteriorgroove 56 formed on the valve stem 18. The plate 50 is releasablysecured to the split clamp 54 by bolts 58 extending through openings inthe clamp 50 to engage tapped holes in the plate 50. An O-ring seal 17,set in an exterior groove of the sheath 29 engages the body 19 toprevent product leakage into the space between the sheath 29 and thevalve stem 18. An air cylinder 28, having an inner end 36 and an outerend 38, has a piston 30 reciprocable therein. The hollow valve stem 18extends through bushings 32 and 34 pressed into the inner and outer ends36 and 38 respectively of the cylinder 28. The valve stem 18 alsoextends through the piston 30, with the piston 30 affixed thereto bybeing trapped between a shoulder 40 formed on the valve stem and a snapring 42. Air under pressure is introduced from a hand-controlled,pressure regulator valve 43 to the outer end of the cylinder 28 througha port 44 provided in the end 34 of the cylinder 28. The other side ofthe piston 30 is vented to atmosphere by a vent port 46 provided in theinner end 36 of the cylinder 28. The leads from the temperaturesensitive tip 26 extend through the interior of the sheath 29 to theweatherhead 60 wherein connection in a conventional manner may be madeto an appropriate display and/or control means in the process controlsystem.

The product flowing from the straight section 10 has two possible paths,one between the valve seat 14 and orifice ring 16 and the other betweenthe orifice ring 16 and tip 26 of the temperature probe 27. The forcecreated by the flow of the product impinging on the frontal area of thetip 26, the end of the body 19 and the orifice ring 16, i.e., thevelocity head, will act to move the valve stem 18 and the attachedpiston 30 toward the left, as viewed in the drawing. Air pressure actingon the outer end of the piston 28 will urge the piston and the attachedvalve stem in the opposite direction. As the flow in the straightsection 10 decreases, the velocity head will decrease. The air pressureacting on the piston 30 will now be greater than the velocity headcausing the piston and the attached valve stem 18 to move to the right.The orifice ring 16 will approach the valve seat 14 decreasing the areaavailable for flow between the valve seat 14 and the orifice ring 16permitting the velocity of product flowing between the orifice ring 14and the tip 26, which would otherwise decrease, to remain constant orsubstantially constant. As the flow in the straight section 10increases, the velocity head will increase, causing the piston and theattached valve stem 18 to move to the left. As a result, the orificering 16 will move away from the valve seat 14 increasing the areabetween the orifice ring 16 and the valve seat 14 and permitting thevelocity of the product flowing past the tip 26, which would otherwiseincrease, to remain constant or substantially constant. Thus, thevelocity of the product flowing past the tip 26 is uniformly maintainedat the desired optimum velocity.

In the engineering of a particular application, the minimum expectedflow through the system is determined based upon ideal design parametersand product characteristics. The orifice is then designed so the orificering 16, even at the minimum expected flow, will be lifted fromengagement with the valve seat 14. The system is then initially operatedunder steady state conditions, i.e., with no variation in flow, at aflow rate at or near the minimum expected and with no pressure beingintroduced by the pressure regulator valve 43 until an equilibrium statein the system is attained, which can be determined by observing a steadypressure at a given point within the system, such as indicated bypressure gage 45. The pressure regulator valve 43 is then graduallyopened to increase the air pressure behind the piston 30. When thesystem pressure begins to increase, as indicated by the system pressuregauge 45, the operator knows the increased system pressure is caused bythe orifice ring 16 approaching the seat 14, and the value of the airpressure causing the slight increase in system pressure will be theproper air pressure for operation of the system. That is, the airpressure acting on the piston 39 is creating a force sufficient to justcounteract the velocity head created by impingement of product on theorifice ring and the temperature probe at the minimum flow rate. Underthese conditions, the orifice ring 16 will be spaced from the seat 14creating the aforementioned two paths. As system flow increases fromthis minimum, the resulting higher velocity head will cause the orificering 16 to move away from the seat 14 permitting a greater percentage ofproduct flow to pass between the orifice ring 16 and the seat 14. Thevelocity of the product through the orifice ring 16 and past the probe27 will, therefore, remain substantially constant. Should the systemflow rate subsequently fall below the expected minimum, the orifice ringwill move, under the force of the air pressure acting on the piston 30,toward the seat 14 to maintain the velocity of product flow through theorifice ring 16 and past the probe 27. Once the proper air pressure hasbeen determined on initial start-up for a particular product, theregulator valve 43 can subsequently be adjusted to that air pressure atthe start of system operations.

The air pressure acting on the piston 30 is in essence an air spring,and is the preferred method of providing a force, because it is aconstant force, to oppose the velocity head created by flow of theproduct. However, some products may permit the use of a compressionspring trapped between the outer end 38 of the cylinder 28 and thepiston 30. The force created by the spring will not be constant, butwill be a function of the distance it is compressed from its relaxedstate. In some cases, such as where the total stroke required is small,this variation in force will provide acceptable performance. When such aspring arrangement is used, the variation in force required fordifferent products may be achieved by substituting compression springswith different spring constants and/or by variation of their relaxedlengths, the latter varying the pre-load on the compression spring. Anextension spring may be used in lieu of a compression spring, with theextension spring having one of its ends attached to the inner end 36 ofthe cylinder 28 and the other of its ends attached to the piston 30.

While a preferred embodiment of the present invention has beenillustrated and described herein, it is to be understood that variouschanges may be made therein without departing from the spirit of theinvention as defined by the scope of the appended claims.

What is claimed is:
 1. A product flow system comprising:a product flowline; a valve seat secured in said line; a valve stem; an orifice ringattached to said valve stem for defining a pair of flow paths forproduct passing through said product flow line, one of said flow pathsbeing through said ring and the other of said flow paths being betweensaid ring and said valve seat; a temperature sensing probe carried bysaid valve stem and positioned in said orifice ring for sensing thetemperature of the product in said line; and a spring connected to acton said valve stem and responsive to changes in velocity of the productin said flow line to move said orifice ring toward and away from saidvalve seat to maintain the velocity of the product flowing past saidprobe substantially constant.
 2. The system according to claim 1,wherein said spring comprises an air spring.
 3. The system according toclaim 1, wherein said spring comprises a compression spring.
 4. Thesystem according to claim 1, wherein said spring comprises an extensionspring.
 5. A product flow system comprising:a product flow line; a valveseat secured in said line; a valve stem; an orifice ring attached tosaid valve stem for defining a pair of flow paths for product passingthrough said product flow line, one of said flow paths being throughsaid ring and the other of said flow paths being between said ring andsaid valve seat; a temperature sensing probe carried by said valve stemand positioned in said orifice ring for sensing the temperature of theproduct in said line; and a spring connected to act on said valve stemfor opposing the force imposed on said orifice ring whereby a smallerpercent of product is directed through said other path in response todecreased flow in said flow line in order to maintain the flow ofproduct through said one path substantially constant.
 6. The systemaccording to claim 5, wherein said temperature sensing probe has atemperature sensitive tip with a forward end, andsaid tip is positionedon the centerline of said orifice ring with said forward end beingpositioned at the minimum diameter of said ring.
 7. The system accordingto claim 6, further comprising:a streamlined body having forward andrearward ends, said forward end including an opening, and said rearwardend being connected to said valve stem; a plurality of support armsconnecting said body to said orifice ring; and said temperaturesensitive tip projecting from said opening.
 8. The system according toclaim 7, further comprising;a clamp for releasably securing saidtemperature probe to said valve stem.
 9. The system according to claim8, wherein said clamp comprises:a plate connected to said temperatureprobe; a split clamp connected to said valve stem; and fastenersreleasably securing said plate to said split clamp.
 10. An apparatus forsensing the temperature of a flowable product moving through a productflow line, the apparatus comprising:a temperature sensing probe adaptedto be disposed in the flowable product; and a valve member connected formovement adjacent said temperature sensing probe, said valve memberresponding to changes in flow velocity of the product moving through theproduct flow line such that said valve member opens in response tohigher flow velocities and closes in response to relatively lower flowvelocities thereby maintaining a substantially constant product flowvelocity past said temperature sensing probe.
 11. The apparatus of claim10, wherein said valve member is operatively connected to a spring andsaid valve member opens against a bias provided by said spring.
 12. Theapparatus of claim 11, wherein said spring comprises an air spring. 13.The apparatus of claim 11, wherein said valve member includes an orificering and further comprising a valve seat, said orifice ring and valveseat defining first and second product flow paths when said orifice ringis opened away from said valve seat, said first flow path being a fixedpath through said orifice ring and said second flow path being avariable flow path between said orifice ring and said valve seat. 14.The apparatus of claim 13, wherein said temperature sensing probe has atemperature sensitive tip with a forward end, said temperature sensitivetip being coaxially aligned with the centerline of said orifice ring andsaid forward end being disposed within said orifice ring.
 15. Theapparatus of claim 10, wherein said temperature sensing probe isselected from the group consisting of resistance thermal detectors,thermistors, bimetallic thermometers, thermocouples and mercurythermometers.
 16. The apparatus of claim 15, wherein said temperaturesensing probe is a resistance thermal detector.
 17. The apparatus ofclaim 10, wherein said valve member further comprises a movable valvestem connected for movement with said temperature sensitive probe.